The present invention relates to fluid pressure operated devices of the type wherein a flexible membrane or diaphragm is responsive to changes in fluid pressure for providing force output to an actuator member which is adapted for connection to perform a mechanical function. Fluid pressure servomotors are often used in applications wherein a vacuum pressure signal is employed to provide control of a mechanical member for a desired function. Vacuum pressure signal operated servomotors have found widespread use in automotive applications where a vacuum or negative pressure signal is readily available, as from an engine manifold depression which generally varies inversely as the load on the engine. Thus, a manifold depression signal may be employed to operate a servomotor to control various devices such as exhaust gas recirculation controllers or engine boost-air inlet valves, or other devices to be controlled in relationship to variations in load on the engine.
In designing and fabricating vacuum operated servomotors for automotive applications where a substantial mechanical force output is required, it is necessary to provide a flexible diaphragm having a substantial area exposed to the vacuum signal in order to provide the desired mechanical force output on the actuating member as, for example, a push rod. In such applications the servomotor output member is often connected to a mechanism, such as a crank arm of a butterfly valve, which produces transverse or arcuate motion of the output member in response to movement in the direction of the output force. This transverse or arcuate motion of the output member results in the reaction applying side loading on the diaphragm, which can cause the return spring on the diaphragm to buckle and permit the diaphragm to rotate within the servomotor and thus can cause damage and premature failure of the diaphragm.
Thus, it has been desired to find a way or means of constructing a fluid pressure actuated servomotor having a flexible diaphragm connected to one end of an actuating output member such that the movement of the actuator when applying sideloads to the diaphragm does not buckle the diaphragm return spring and result in consequent adverse rotation of the diaphragm.